Effects of Nondeterminism in Hardware and Software Simulation with Thread Mapping

In this paper, we explore the simulation performance trade-off under the lens of Monte Carlo design space exploration for multi-threaded programs and thread mapping. The vehicle used for this exploration will be a recent study, whose novel Google Page Rank-based thread mapping approach is compared to hundreds of random mappings, as well as a Round-Robin-based thread mapping approach proposed in this paper used in similar comparisons. The modern simulator landscape presents a choice between cycle-accurate but slow, and fast but inaccurate program simulation. We find that the use of a fast, inaccurate multi-threaded simulator, such as Sniper 5.3, suffers from large nondeterminism in the reported performance of the program. We perform cycle-accurate simulation which demonstrates that the static thread mapping approach does provide benefits in reaching near-optimal design points. Furthermore, the runtime of static thread mapping is significantly reduced using a cycle-accurate simulator compared to the full Monte Carlo exploration of mapping design points.